The concept of a "Kickstarter.gov"

The Mars Rover, Curiosity, landed last night, it's a huge achievement for mankind, even though it isn't the first Mars Rover. It's mechanical grandeur and scientific poise are yet to come, though, the real excitement will be in the next few days as the MSL (Mars Science Laboratory) starts working.

A blog I was reading, which had an article about the MSL said that the 2.something billion dollar mars mission only came to $7 per taxpayer. And I was like "WTF! I would pay more than THAT!"
Which gave me this idea.

What if Governments gave the informed and socially responsible citizens the choice– 

–not only of who to lead our country and our states, cities and towns– 

–but also of where the taxes we pay go. 

Like the website Kickstarter, people would pledge money toward government projects and facilities. Unlike Kickstarter, where the users are rewarded at different levels of spending, every taxpayer would simply get the thing they pledged toward, be it the library or the moon landing, this time on Io or Europa. Taxpayers would become funders, the very thing we are, but our money is taken and applied to whatever the government thinks is important, not what we want to use. 

Maybe the government would say "Each taxpayer is required to spend X money on Y number of city projects, Z amount on state projects and W amount on national projects. 

 

That sounds good right. It's not a constitution, but I think it has promise.

Feel free to comment with suggestions or even something like a complete overhaul of this form of democracy.
Also, what would you put your money into if your government had this policy?